February 01, 2014
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Dislocation after THA remains a dreaded complication for patients and surgeons

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Total hip arthroplasty is one of the safest and most effective orthopaedic surgeries, but despite continued improvements in surgical technique and implant design, complications persist. Dislocation after total hip arthroplasty is a sometimes devastating complication that can seriously affect a patient’s quality of life and today it is possibly the most common problem that can occur after total hip arthroplasty.

The management of an unstable hip can challenge the most experienced orthopaedic surgeon. In this article, leading hip surgeons in Europe discuss who is at greatest risk for dislocation after total hip arthroplasty (THA) and offer some optimal ways they have used to treat THA dislocation and suggest methods to prevent it.

“There is no doubt that dislocation is important,” Fares S. Haddad, FRCS (Orth), Professor of Orthopaedic and Sports Surgery at University College Hospital in London and member of the Orthopaedics Today Europe Editorial Board, said. “It is a common complication. It is a highly feared complication by surgeons because ... if a dislocation happens, surgeons perceive it as their problem, as something they could have avoided.”

Fares S. Haddad, FRCS (Orth)
Fares S. Haddad

It is also an expensive problem.

“If you look at it overall in terms of the number of admissions and operations, it is as expensive as any of the other complications that require revision,” Haddad said.

And even with successful treatment, many clinicians note that the outcome of dislocation treatment never matches the results of an uncomplicated primary THA.

“Once the patient has a dislocation, even if it doesn’t dislocate again ... they lose confidence in their hip,” Haddad told Orthopaedics Today Europe. “They are not as happy as patients who don’t dislocate,” he said.

Incidence of dislocation

The incidence of dislocation following THA is variable and is dependent on multiple factors, such as geography, surgery type and surgeon.

“It is obviously a common problem,” Haddad said. “If you look at our data or [those of] the Hospital for Special Surgery or Mayo Clinic for primary replacement, the incidence of dislocation is now well under 1%. If you look at certain centers in the published data from Bristol, for example, it is up to about 4% in primaries. In revisions, worldwide it is about 10%.”

There are several reasons for the wide range of dislocation incidence rates and they include surgical techniques, components and approaches used.

“High-volume surgeons would tend to have a more refined technique that limits the risk of dislocation,” Haddad said. “It is partly related to the approach that people use. It is partly related to the size of the head that people use. I think the key is implant positioning and the quality of the surgery,” he said.

Early and late dislocations

After primary THA, patients are most likely to dislocate during the first 6 weeks to 8 weeks following surgery when the soft tissues are still healing, according to A. John Timperley, FRCS (Ed), DPhil (Oxon), president of the British Hip Society and a consultant orthopaedic surgeon at Princess Elizabeth Orthopaedic Hospital, in Exeter, United Kingdom.

Although most dislocations occur during the immediate postoperative period, patients have a lifetime risk for dislocation.

“You just can’t consider dislocations in the immediate aftermath of surgery because patients continue to have a dislocation risk over time,” Haddad said. “The Mayo group, in particular, chronicled late dislocations. The concept is that beyond the first couple of years, there is a 1% per year dislocation risk that goes up.”

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Several factors put an individual at greater risk for a THA dislocation, according to Moussa Hamadouche, MD, PhD, professor of orthopaedic surgery at Hopital Cochin in Paris. The patient-related factors, he said, include the following:

  • advanced age (older than 75 years);
  • gender (elderly women are more at risk);
  • cognitive dysfunction (dementia or Alzheimer’s disease);
  • alcohol or drug abuse;
  • neuromuscular diseases, such as Parkinson’s; and
  • underlying diseases, like avascular necrosis.

“All of these are patient-related; they are well known and well recognized in the literature as risk factors for dislocation,” Hamadouche told Orthopaedics Today Europe.

Surgical risk factors

Implant malposition is the primary surgical risk factor, Hamadouche said. Other surgical risk factors that he discussed included reduced offset, leg length discrepancy and using small-diameter femoral heads.

Moussa Hamadouche, MD, PhD
Moussa Hamadouche

These factors can all lead to impingement, which is a leading cause of hip dislocation following THA, he said.

Surgical approach is an important factor, as well, in relation to THA dislocation and instability.

“The posterior approach, although it is the most popular approach around the world, is a risk factor,” Hamadouche said. “When you use the posterior approach, you are going to cut the posterior tendons, especially the piriformis. Once the tendon is cut, healing is not always perfect, and you have a hole on the back of the articulation,” he said.

Some orthopaedic surgeons believe the anterior approach to THA — because theoretically it provides greater stability — may be a good alternative to the posterior approach. “Every new technique is associated with some problems,” Haddad said. “The issues are the anterior approach has a big learning curve. And, if you look at the Norwegian Registry data, the anterior approach is associated with a higher risk of dislocation. It is not necessarily the answer, [but] it is a promising technique,” he said.

Evaluation of hip dislocation

Johan Kärrholm, MD, PhD
Johan Kärrholm

The first step in evaluating a patient with a THA dislocation is to listen to the patient, said Per Kjaersgaard-Andersen, MD, chief medical editor of Orthopaedics Today Europe.

“If they can tell you about subluxation — they have the feeling that the hip is out and suddenly it is in again — then this is a subluxated hip,” Kjaersgaard-Andersen, of Vejle, Denmark, said. “If they tell you this, then you should rely on it,” he said.

Another important step is “an ordinary and well-performed radiographic examination,” Johan Kärrholm, MD, PhD, a professor in the department of orthopaedics at Sahlgrenska University Hospital, in Gothenburg, Sweden, said. He told Orthopaedics Today Europe, “If you have good X-rays, you can evaluate the position of the implant fairly well. If you are in doubt, you can perform a CT [to] look at the anteversion of the femoral component.”

A new technology, which involves low-dose 3-D musculoskeletal imaging (EOS imaging SA, Paris), may prove to be a good tool for diagnosing hip dislocations and instability problems. With it “[you can get] AP and lateral views of the whole body [with] very low exposure rates,” Hamadouche said. “And, you can do these radiographs while the patient is standing and sitting. It gives you more insights into the position of the components.”

Dislocation treatment varies

The surgeon’s treatment of choice in these cases depends on the cause and timing of the dislocation. Most patients with an early dislocation, however, can be treated with a simple closed reduction.

“For a group of patients with well positioned implants who dislocate through a false maneuver, it is perfectly reasonable to just pop the hip back in and then restrain them for a while to let the soft tissues heal and rehabilitate,” Haddad said.

But in other early dislocation cases, surgery is needed immediately.

“If I see that the acetabular component is in the wrong position, I will always recommend that the patient have surgery as quickly as possible to reposition the acetabular component because they will be a repeat dislocator,” Kjaersgaard-Andersen told Orthopaedics Today Europe.

Patients who have recurrent dislocations require surgery. “Most people who dislocate in the early postoperative period, only dislocate once,” Timperley said. “But there is a group who goes on to recurrent dislocation. That is the group that you would discuss further surgery with,” he said.

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Dual mobility cups

In Europe, one popular treatment option that many orthopaedic surgeons use is a dual mobility cup. The dual mobility cup features two articulations: a small articulation between the femoral head and the mobile bearing — which is where most of the movement occurs — and a large articulation between the mobile bearing and the acetabular component. The large articulation acts like an ultra-large diameter femoral head.

“There have been a number of papers showing that both in primaries for patients who are at risk and in revision, it does really reduce the risk of dislocation,” Hamadouche said.

Short-term data from the Swedish Hip Arthroplasty Register showed that dual mobility cups had a low risk of re-revision when used in revision THA performed for recurrent dislocations. Hailer and colleagues recently identified 228 THA cup revisions that were performed due to recurrent dislocations. Fifty-eight patients had undergone revision at least once before the index cup revision. In 99 cases, the surgical approach used for the index cup revision was lateral; it was posterior in 124 cases. At the median 2-year follow-up, 18 patients had been re-revised for any reason and four of these patients were re-revised for dislocation.

Two-year survival, with the endpoint being revision of any component due to dislocation, was 99% (95% CI, 97-100), and it was 93% (95% CI, 90-97) with the endpoint of revision of any component for any reason.

Typically, dual mobility cups have been reserved for at-risk patients who are aged older than 70 years. A prospective, multicenter study by Epinette and colleagues that investigated second-generation dual mobility cups showed that at 2 years to 5 years follow-up two groups of patients demonstrated good results: patients aged younger than 70 years (112 hips) and patients aged older than 70 years (325 hips). Neither group had evidence of dislocation, migration, tilting, wear or intra-prosthetic dislocation. Survivorship was 100% in the younger patients and 99.7% in the older patients, according to results of the study.

A focus on prevention

Because it is potentially devastating, preventing post-THA dislocation is critical.

“I think the first thing is to plan the surgery adequately,” Timperley said. “A lot of surgeons don’t template every procedure. I think every X-ray needs to be scaled and templated, so that the first thing to do is to make sure you plan to put the center of rotation where it should be and create offset and correct leg length for the patient.

“With a lot of hip systems, it is not easy to do that,” Timperley continued. He noted it is difficult to match the offset to the femur size with uncemented systems. “That is one reason I use cemented femoral components,” Timperley said. “When you use a cemented femoral component, stem size, offset, leg length and version are completely independent variables.”

Surgeons at Kjaersgaard-Andersen’s clinic template all of their cases.

“This is important to get the correct offset, [and] to get the tension of the soft tissue to the correct level,” he said.

Correct acetabular component positioning is equally important because it avoids impingement, one of the major causes of dislocations, according to Timperley.

Haddad said there are several other keys to prevention, as well. First, correctly identify the most at-risk patients. Second, perform an excellent bony and soft tissue repair. Third, choose larger head sizes — up to 32 mm and 36 mm — because they are more stable than smaller head sizes.

Another study by Hailer and colleagues based on Swedish Hip Arthroplasty Register data showed revision risk was higher when 22-mm femoral heads were used for THA. Most importantly, the primary T HA surgery should be tailored to the patient’s age and level of function and activity.

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“The requirements of a 50-year-old active man who is going to rehabilitate well are very different from those of an 85-year-old frail lady who has hypermobility,” Haddad said. – by Colleen Owens

Disclosures: Haddad is a consultant with Smith & Nephew, Stryker, MatOrtho and Corin. Hamadouche is a consultant for Smith & Nephew, Medacta, BBraun, Aston Medical and Mathys. Kärrholm has no relevant financial disclosures. His institution receives research support from Zimmer Europe, Link, Biomet and DePuy Synthes. He is member of the board of RSA Biomedical. Kjaersgaard-Andersen has no relevant financial disclosures. Timperley has intellectual property invested in a hip system with Stryker.

POINTCOUNTER

When is surgery indicated to correct an early dislocated THR?

POINT

Surgery is recommended in select cases

Dislocation is the first cause of surgical revision for a total hip replacement (THR) in the United States, Australia and New Zealand, the second cause of revision in the Swedish Hip Arthroplasty Registry and the fourth cause in the United Kingdom. Nevertheless, in most cases closed reduction and immobilization in a hip brace for 3 weeks to 4 weeks is the gold standard for a first-time dislocation. In some cases, however, a surgical reduction becomes necessary.

Roberto Binazzi, MD
Roberto Binazzi

The indications for open reduction of an early dislocated THR are all cases that are unreducible manually, when the manual reduction cannot be maintained, or when X-rays indicate the problem can be fixed only surgically. Component malposition is the most frequent cause with an excessively vertical cup or excessive anteversion or retroversion of the cup and/or the stem, but breakage or undersizing and/or instability of the components is also common. Impingement that is produced by posterior osteophytes, cement or soft tissue interposition is a less frequent cause.

Surgical treatment is obviously etiologic and should aim to correct the factors that have caused the instability. Various surgical options include revision of the components, bipolar arthroplasty, exchange of modular components (head and liner) or use of a constrained liner. In all cases, it is advisable to carefully reconstruct the peri-articular soft tissues.

Roberto Binazzi, MD, is chairman of the department of hip surgery at Villa Erbosa Hospital, Bologna, Italy.
Disclosure: Binazzi has no relevant financial disclosures.

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COUNTER

Incidence of recurrent instability may exist

Instability following THR is a frequent and serious problem, which requires thorough evaluation and planning before further surgical intervention. The procedure is challenging even for experienced surgeons, but even after a well-planned surgery a significant incidence of recurrent instability may exist.

In patients with immediate or secondary reluctant dislocation and obvious component malalignment, surgical revision should be a strong consideration. It is important to identify and address the cause or causes of dislocation at the index revision operation. In addition, soft tissue tension plays a key role as it is influenced by capsule and muscles, in particular the short external rotators and gluteal muscles. On the other hand, appropriately placed components may become unstable if appropriate leg length and hip offset are not restored and if they are not properly combined with the anteversion. These factors are important for decision making to address an early dislocated THR since patients with a loss of offset are more likely to dislocate.

Manuel Ribas, MD
Manuel Ribas

Surgical options for the treatment of instability include revision of components; exchange of modular components, such as the femoral head and acetabular liner; the use of bipolar–tripolar arthroplasty; larger femoral heads; and constrained liners. Capsular and muscle reattachment, in particular with the posterior approach, have been shown to reduce dislocation rates significantly. If the soft tissues are lax and the offset has already been maximized, a lateralized liner can increase soft tissue tension, as well as soft tissue reinforcement and advancement of the greater trochanter.

Manuel Ribas, MD, is an orthopaedic surgeon and traumatologist. He is head of the hip unit at USP-Dexeus University Institute, in Barcelona, Spain.
Disclosure: Ribas is a consultant to and receives implant design royalties from Wright Medical Technology and Microport and he is a consultant to Conmed Linvatec and Adler Ortho.

COUNTER

Surgical management may not be necessary

Early surgical intervention should be avoided unless there is an obvious mechanical obstruction to closed reduction. Normally this is achieved under anesthesia with muscle relaxation, but must be monitored with radiological screening to detect any implant loosening or impingement and to check post reduction stability.

Bed rest with an abduction wedge and anti-rotation boot is used until the patient has recovered muscle control and is pain free. This allows time to identify the factors responsible for instability and to discuss the implications of any surgical solution with the patient.

A review of the operative record and postoperative X-rays should identify prosthetic misalignment or impingement. If present, the case for surgical intervention is strengthened, though this should be deferred until a second dislocation has occurred. It is then essential that the surgical procedure selected offer a lasting solution, rather than leaving a high risk of further instability. The problem is that the optimum result may require a major complex revision operation, which can be inappropriate in an older patient with poor soft tissues, inadequate bone stock and numerous comorbidities.

David L. Hamblen, PhD, FRCS
David L. Hamblen

The surgical options available in order of magnitude and success rates are as follows:

  • Repair of abductor muscles and capsule;
  • Correction of femoral and/or cup misalignment;
  • Insertion of constrained cup liners or large femoral heads;
  • Acetabular cup augmentation; and
  • Insertion of a new dual mobility prosthesis.

The final choice may depend on the experience of the surgeon and may necessitate referral to a Specialist Unit.

David L. Hamblen, PhD, FRCS, is emeritus professor of Orthopaedic Surgery, University of Glasgow, and Emeritus Consulting Editor of Orthopaedics Today Europe.
Disclosure: Hamblen has no relevant financial disclosures.